From: Eliot Miranda <eliot.miranda@gmail.com>
Date: October 29, 2018 at 11:53:37 AM PDT
To: The general-purpose Squeak developers list <squeak-dev@lists.squeakfoundation.org>
Subject: Re: [squeak-dev] What should Integer>>digitCompare: return?
On Oct 29, 2018, at 11:46 AM, Eliot Miranda <eliot.miranda@gmail.com> wrote:Hi Chris,On Oct 28, 2018, at 3:41 PM, Chris Cunningham <cunningham.cb@gmail.com> wrote:Looking at LargeIntegers (I'm 64 bit, so these are big):{1152921504606846977 digitCompare: -1152921504606846977.1152921504606846977 digitCompare: -1152921504606846978.1152921504606846978 digitCompare: -1152921504606846977.} "#(0 -1 1)"{1249 digitCompare: -1249.1249 digitCompare: -1250.1250 digitCompare: -1249.} #(1 1 1)this is correct. The primitive is supposed to answer -1, 0 or 1 depending on whether the (receiver digitAt: n) is <, =, or > the (argument digitAt: n) where n is either the first digit at which the receiver and argument differ or the last digit. Since digitAt: does not answer the 2’s complement bit-anded SmallIntegers are not actually inconsistent-1 digitAt: 1 => 1-1 digitAt: 2 => 01 digitAt: 1 => 11 digitAt: 2 => 0SmallInteger minVal - 1 digitAt: Smalltalk wordSize => 16 (64-bits) 64 (32-bits)SmallInteger maxVal + 1 digitAt: Smalltalk wordSize => 16 (64-bits) 64 (32-bits)
or more clearly:
(SmallInteger minVal digitCompare: SmallInteger maxVal + 1) = 0
As the comment says, digitCompare: compares the magnitudes, not the 2’s complement representations.So the method needs a) a really good comment and b) a warning that this is private to the Integer hierarchy implementation and not for general use.It looks to me like the use in DateAndTime is a hack that works because LastClockValue is always +ve._,,,^..^,,,_ (phone)